In a compressor of the type driven by a linear motor, the gas compression and gas suction operations are performed by the axial movement of a piston inside a cylinder, which is closed by a cylinder head and mounted inside a hermetic shell, in the cylinder head being positioned a discharge valve and a suction valve, which control the admission and discharge of gas in the cylinder. The piston is driven by an actuating means that carries magnetic components such as an electrical coil, which is exposed to a magnetic field generated by a magnetic element, such as a magnet, and operatively associated with a linear motor affixed to the shell of the compressor.
These constructions generally present two helical springs under constant compression and which are operatively mounted against the actuating means, each seated against an adjacent surface of the latter. The piston, the movable parts of the actuating means, the magnetic components, and the helical springs form together the resonant assembly of the compressor, which is driven by the linear motor and has the function to develop a reciprocating linear movement, making the movement of the piston inside the cylinder exert a compression action on the gas admitted by the suction valve, until a point is reached in which said gas is discharged to the high pressure side, through the discharge valve.
The reciprocating movement of the piston requires a lubrication system to minimize frictions and wears, in order to assure an adequate performance to the compressor.
In constructions known from the art, the supply of lubricant oil to the cylinder and piston is made through a lubrication system using the principle of centrifugal force and mechanical drag, with channels contained in the cylinder, such as presented in document PI0004286-2, of the same applicant, or in documents WO97/01032 and WO97/01033. These channels are of complex construction, due to the difficult access to the lubricated region and require careful sealing, since they pass through some components.
In one of the known solutions, in order to supply oil to the piston/cylinder assembly, it is necessary to make the compressor suction gas flow, which generates a small pressure differential in relation to the oil sump, to draw said oil through a capillary tube, mixing it with the gas drawn by the compressor, said mixture being admitted to the inside of the cylinder by the suction valve, so that the oil lubricates the contact regions between the piston and the cylinder. As a function of the low gas flow drawn by the compressor in certain situations, this construction presents low efficiency regarding lubrication.
In another known construction (WO97/01033), the compression and suction forces of the piston are used to displace the lubricant oil from the sump, through a capillary tube, to an upper reservoir formed around the cylinder, said upper reservoir being connected to the inside of the cylinder by a plurality of orifices formed in the wall of the latter and which serve for admitting oil into the piston-cylinder gap, when the piston is performing the suction movement, and for discharging said oil when the piston is performing the reverse movement. The oil is discharged into a number of channels formed in the valve plate of the compressor, further supplying the suction flow, causing said oil to re-enter the cylinder.
Other known solution (WO97/01032) uses a resonant mass that moves reciprocally inside a cavity formed in the external side of the cylinder, said resonant mass drawing oil from the sump while moving in one direction, said oil passing through a tube and through a check valve, which allows only the admission of oil into said cavity, the latter being connected to the inside of the cylinder by a plurality of orifices formed in the wall thereof. The oil in said cavity is expelled when the resonant mass moves in the other direction and passes through a check valve, which allows only the discharge of oil from said cavity. Although being functional, this solution is difficult to manufacture and its construction presents many components.